Based on the surface plasmon resonance of metal and anti-resonant principles of hole-core microstructure optical fiber (MSF), in this Letter, we demonstrate a MSF microfluidic sensor that combines silver film and hole-core MSF to achieve the sensitive real-time monitoring of refractive indices and components. The large hole core is a common channel for guiding light and flowing measured liquid. Because of the interaction between light and continuous flow measured liquid, the component and refractive indices can be simultaneously monitored by the characteristic absorption wavelength and the surface plasmon resonant peak position, respectively. These results indicate that the MSF microfluidic sensor is an ideal multi-parameter measurement optical sensor.

In this work, Tm:YAG (Tm: Y 3 A l 5 O 12 ) ceramic-derived multimaterial fiber was fabricated by using the molten core method, which has a high gain per unit length of 2.7 dB/cm at 1950 nm. To our knowledge, this is the highest gain per unit length at 2 µm band in similar Tm:YAG-derived multimaterial fibers. A distributed Bragg reflector (DBR) fiber laser was built based on a 10-cm-long as-drawn fiber. The achieved 1950 nm laser, which has a maximum output power of ∼ 240 m W and a slope efficiency of 16.5%, was pumped by a self-developed 1610 nm fiber laser. What is more, an all-fiber-integrated passively mode-locked fiber laser based on the 10-cm-long as-drawn fiber was realized. The mode-locked pulses operate at 1950 nm with duration of ∼ 380 p s , and the repetition rate is 26.45 MHz. The results described here indicate that the Tm:YAG ceramic-derived multimaterial fiber with high gain per unit length has promising applications in 2 µm all-fiber fiber lasers.

An ultrahigh sensitive optical fiber sensor for trace detection of Cu²⁺ concentration in aqueous solution with temperature calibration has been developed in this article. Based on the intermodal interference, the sensor is coated with a hydrogel sensing membrane with specific binding to Cu²⁺ on the no-core fiber/single mode fiber/no-core fiber structure by using our new spray coating method. The imidazole group in the sensing film combines with Cu²⁺ to produce chelation, which changes the refractive index of the sensing film. The Cu²⁺ at trace concentration can be detected by monitoring the displacement of the interference trough. The experimental limit of detection of 3.0×10⁻¹² mol/L can be achieved with the spectral resolution of 0.02 nm. The sensor has also long-term stability of the concentration measurement with the average standard deviation of 1.610×10⁻¹² mol/L over 2 hours observation time and can be compensated the influence of ambient temperature on concentration detection by conducting the temperature calibration. In addition, the sensor has the advantages of strong specificity, simple fabrication and low cost.

In this paper, a dual hollow-core negative curvature fiber is proposed for the polarization beam splitter. The effects of the structure parameters of the dual hollow-core negative curvature fiber on the coupling length and coupling length ratio of the x -polarized and y -polarized core modes and the higher-order mode extinction ratio are analyzed by the finite element method. Moreover, the normalized output powers of the x -polarized and y -polarized modes in the cores A and B and the corresponding extinction ratio are also investigated by the mode coupling theory. The simulation results show that a dual hollow-core negative curvature fiber polarization beam splitter with the length of 6.45 cm can achieve a broad bandwidth of 400 nm (1.23–1.63 µm), covering the O + E + S + C + L communication band. In addition, the higher-order mode extinction ratio is greater than 100 in the considered wavelength range, which means that it has good single-mode characteristics. It is believed that the proposed dual hollow-core negative curvature fiber polarization beam splitter will have significant applications in the optical communication system.